A typical facsimile machine or copy machine can receive a stack of paper sheets for reading or copying and automatically feed one sheet at a time from the stack for further processing by the machine. One well known paper separation technique uses a single paper-feed roller made of rubber or other high-friction material. One or more paper-feed springs (usually a leaf spring) opposes the roller. When a stack of paper is properly placed into a paper tray, the edge of the stack of paper is wedged between the high friction roller and the paper-feed springs. When the roller begins turning, while the paper-feed springs press the stack of paper against the roller, the bottommost sheets will be forwarded by action of the roller while the top sheets will be generally restrained by the angle of the paper-feed springs. Frequently, two or more sheets of paper are forwarded beyond the paper-feed springs and must be separated from one another.
In order to separate these two or more sheets from one another and only forward the bottom sheet, a separator pad formed of rubber is located downstream from the paper-feed springs. A separator spring biases the separator pad against the paper-feed roller or against a downstream roller. A downward force of the separator pad against the top sheets now frictionally grips these top sheets. The greater frictional force provided by the paper-feed roller against the bottom sheet now causes only the bottom sheet to be forwarded beyond the separation pad for further processing.
Examples of such techniques are described in U.S. Pat. Nos. 4,887,806 and 4,674,737.
The high-friction paper-feed rollers used in these types of devices are cylindrical with no perceptible asymmetry so as to provide a relatively constant forwarding force to the paper sheets.
Despite extensive experimentation and optimization of design, these prior art paper separation systems are still subject to malfunctions where two or more sheets of paper at a time are forwarded beyond the separation pad. One reason for such malfunctions is that the various users of the facsimile or copy machine insert the stack of sheets against the paper-feed roller with varying forces. This affects the initial friction between the roller and the bottom sheets, as well as the friction between the sheets themselves. Another reason for such malfunctions is due to the varying characteristics of the paper itself stemming from humidity, paper smoothness, and other obvious factors which affect the amount of force needed to separate one sheet of paper from another sheet of paper.
What is needed is an improved structure and technique for automatically separating a bottom or top sheet of paper from a stack of paper inserted into a facsimile machine, a copy machine, or the like. It would also be extremely advantageous that this structure easily replace existing structures in such machines to improve the paper separation capability of these machines at a minimum of cost.